PROJECT SUMMARY Sepsis accounts for approximately 8% of pediatric intensive care unit (PICU) admissions, with an in-hospital mortality of 25% and an estimated annual cost of $4-5 billion in the United States. Delayed antimicrobial therapy is associated with worse outcomes for pediatric sepsis, but initial signs of sepsis can be non-specific and subtle. Clinicians frequently order blood cultures to aid in diagnosing bacterial sepsis, but universally accepted standards or guidelines to guide decisions around when to obtain blood cultures are not available. Weighed against the potentially disastrous consequences of failing to diagnose sepsis in a timely fashion, blood cultures are generally perceived to be a low-risk screening test. The yield of blood cultures, however, is low (5-15%) and up to half are falsely positive. False positive cultures contribute to patient harm via additional hospital days, unnecessary antibiotics, and increased costs. Unnecessary antibiotic use is a primary driver of antibiotic resistance, which is emerging as a grave threat to human health worldwide. Recently, a novel clinical practice guideline designed to standardize approach to blood cultures in critically ill children safely reduced blood culture use by 46%. In addition, there was a 15% reduction in broad spectrum antibiotic use post- intervention. Subsequent implementation of this program in two other PICUs yielded reductions in blood culture use. The long term objective of this proposal is to determine whether diagnostic stewardship, specifically the appropriate use of blood cultures, can safely reduce antibiotic use and antibiotic resistance in a large and diverse group of hospitals. The specific aims are Aim 1) to implement an evidence-based, clinical practice guideline for evaluation of patients with signs and symptoms of sepsis to decrease blood culture use in PICUs, Aim 2) to evaluate whether a clinical practice will reduce antibiotic use, antibiotic resistance, and Clostridium difficile infection, and Aim 3) to determine whether this clinical practice guideline has an unintended consequence of patient harm. A prospective multicenter quality improvement program will be implemented at 10 hospitals, and will be evaluated using a quasi-experimental design comparing outcome data in pre- and post-periods. The findings could provide evidence that diagnostic stewardship around blood cultures can decrease harm to patients by reducing unnecessary antibiotic use and antibiotic resistance.